Circuit arrangement for frequency controls



Npv. 21, 1950 E. SCHOLTEN CIRCUIT-ARRANGEMENT FOR FREQUENCY CONTROLSFiled June 7, 1946 1NVENTOR.-

EGBERT SCHOLTEN BY A ATTORNEY Paten tecl Nov. 21, 1950 UNITED STATES r.

TENT OFFICE CIRCUIT ARRANGEMENT FOR FREQUENCY CONTROLS Application June7, 1946, Seriai No. 675,023 In Belgium February 8, 1945 Section 1,Public Law 690, August 8, 1946 Patent expires February 8, 1965 6 Claims.(Cl. 250-36) This invention relates to a circuit-arrangement forcontrolling with the aid of a control magnitude the frequency ofelectrical oscillations generated by means of a discharge system, thiscircuit being particularly suitable for keeping constant the frequencyof telegraphy transmitters and for the production of frequency-modulatedoscillations.

Circuit-arrangements are known in which the frequency of the electricaloscillations produced by an oscillator is controlled in accordance withthe value of a control voltage, a so-called reactance tube being used.Such a tube which may be connected in parallel with the resonant circuitof the oscillator behaves as a reactance depending upon the mutualconductance. To this end the tube is connected in such a manner that thealternating voltage of the grid, to which the control voltage issupplied and the anode voltage of the tube exhibit a phase-difference ofabout 90.

These circuits have the drawback that, if the frequency of theoscillations produced should be variable through a fairly considerablerange, the power of the reactance tube should be of the same order ofmagnitude as that of the oscillator tube. With a high power oscillatoruse should consequently be made of a reactance tube capable of absorbinga high power which is not economical.

The invention procures a circuit-arransement which permits the frequencyof the oscillations produced to be varied through a comparatively broadrange, without an additional high power tube being needed. According tothe invention the frequency of the oscillations produced is controlledby inserting an impedance in a lead to a control-electrode of theaforesaid discharge system, the magnitude of this impedance varying withthe control magnitude.

Use is preferably made of a discharge tube to constitute the impedance,which tube is controlled by the control magnitude (control voltage,modulation voltage). Thus a simple circuit ensues, in which acomparatively low power discharge tube permits the frequency to becontrolled over a wide range.

If the invention is used in a circuit-arrangement for keeping constantthe frequency of the electrical oscillations produced by means of adischarge system, the said impedance or the said discharge tube caneffectively be controlled by means of a control voltage initiating froma frequency detector to which the produced oscillations are supplied.

In order that the invention may be clearly understood and readilycarried into effect, it will now be explained more fully with referenceto the accompanying drawing, in which one form of construction thereofis represented by way of example.

Referring to the drawing there is shown an oscillator circuit having anelectron discharge tube I, which in the present example is shown as atriode, by means of which the electrical oscillations are produced whosefrequenc is kept at a constant value. The anode-circuit of tube lincludes a resonant circuit 2 which is inductively coupled with aback-coupling coil 3 which is inserted, in series with a condenser 4, inthe control-grid circuit of tube I.

According to one embodiment of the invention the lead from the controlgrid to the oathode of tube I includes a discharge tube 5. In serieswith tube 5 are connected a cathode resistance 6 and a choke I; theseries-connection 5, 6 and '5 functions as a leakage resistance for thedischarge tube I. Furthermore, the grid circult of tube 5 comprises agrid leakage resistance 8. A condenser 9 shunts the tube 5 in regard tocurrents of the oscillations generated. The frequency of the electricaloscillations produced by the oscillatory system I, 2, 3, 4 is controlledby varying the resistance of tube 5. This is effected by means of acontrol voltage which is supplied to the control grid of tube 5 and moreparticularly to the terminals designated by ID.- In the present casethis control voltage is taken from a frequency-detector H to which theoscillations generated by the circuit 2 are applied, for example, bymeans of a Winding IL.

The operation of the circuit is based on the fact that the frequency ofthe oscillations generated by means of a discharge tube by backcouplingdepends, inter alia, upon the value of the grid-current, so that bycontrolling the value of this current (which in the present case takesplace by controlling the value of the leakage resistance) the frequencyof the oscillations is affected.

The influence of the value of the grid current on the frequency of theoscillations generated can. be increased by causing a phase-displacementmaterially differing from to take place between the voltages set up atthe oscillator electrodes of the discharge system. For thispurpose theback-coupling circuit of the present arrangement comprises aphase-shifter which, in the case under view, consists of the condenser4- and the internal resistance between grid andcathode of the tube I. Inconjunction therewith the condenser 4 is a condenser having a lowcapacity (for example about 40 micromicrofarads at a frequency of 3mc./s., whereas the normal value is 300 micromicrofarads) Owing to thephase-displacement brought about by the element the frequency of theoscillations generated no longer coincides with the resonance frequencyof the resonant circuit 2. In fact, this adjusts itself so far from theresonance frequency that across the circuit 2 occurs a substantially asgreat, but opposite phase displacement as across the back-couplingcircuit. If, consequently, the magnitude of the phasedisplacement acrossthe back-coupling circuit is changed, the frequency of the oscillationsgenerated varies at the same time.

By control of the direct grid current of tube I, which in thecircuit-arrangement shown is effected by controlling the resistance oftube 5, the internal resistance between grid and cathode of the tube isvaried; as a result thereof the phase-displacement across theback-coupling circuit. varies (i. e. the phase of the alternatingcontrol-grid voltage) which, as has been set out above, brings about avariation of the frequency of the oscillations generated.

At a control voltage of volt the frequency of the oscillations generatedis adjusted approximately at the centre of the desired control range.This may, for instance, occur by adjustment of the cathode resistance 6or by giving the control tube a suitable bias.

Now, if the control voltage assumes a value deviating from zero, thevalue of the leakage -resistance constituted by the control tube 5varies likewise, with the result that the frequency of the oscillationsgenerated by means of the oscillator tube I is varied. The controlvoltage should, of course, be supplied to the terminals l0 in such amanner that, if for example, the frequency of the oscillations generatedshould tend to increase, the resistance variation of tube 5 shows atendency to counteract this frequency increase.

The circuit-arrangement may advantageously be used for keeping constantthe frequency of telegraphy transmitters, since the frequency of theoscillations transmitted varies due to the signalling. These frequencyvariations can be suppressed completely or substantially completely byusing this circuit-arrangement.

The invention may also be used to generate frequency-modulatedelectrical oscillations. In this case the modulation voltage mayeffectively be supplied to the terminals ll) of the circuit shown in thedrawing.

It may still be observed that by controlling the internal resistance oftube 5 the direct grid current of tube I is varied, but the direct gridvoltage of this tube remains substantially constant. If, consequently,the circuit-arrangement is used for the production offrequency-modulated oscillations a highly linear, distortion-freefrequencymodulation is ensured without a material amplitude-modulationoccurring.

What I claim is:

'1.A' 'circuit'arrangement for varying'the frequencyof an oscillator inresponse to variations of a control voltage, comprising an oscillatortube having an anode, a control grid and a cathode, a resonant circuitcoupled between the anode and cathode'of'said oscillator tube todetermine the frequency of'said oscillator, a coil inductively coupledto said resonant circuit; means coupling said coil between the grid andcathode of said oscillator tube to couple the grid in feedbackrelationship substantially out of phase with respect to the anode ofsaid oscillator tube, a variable impedance element coupled between thecathode and the control grid of said oscillator tube, and meansresponsive to said variations of said control voltage to vary theimpedance value of said impedance element thereby to effect a shift inphase away from said 180 relationship and vary the frequency of saidoscillator.

2. A circuit arrangement for varying the frequency of an oscillatorabout a determined frequency value in response to variations of acontrol voltage, comprising an oscillator tube having an anode, acontrol grid and a cathode, a resonant circuit coupled between the anodeand cathode of said oscillator tube to determine the frequency of saidoscillator, a coil inductively coupled to said resonant circuit, acapacitor coupling said coil between the grid and cathode of saidoscillator tube to couple the grid in feedback relationship to the anodeof said oscillator tube, a control tube having an anode, a grid and acathode, the anode of said control tube being coupled to the cathode ofsaid oscillator tube, a first resistor, a second capacitor, means toconnect said first resistor and said second capacitor in series betweenthe grid of said control tube and the cathode of said oscillator tube,means to apply said control voltage across said first resistor, a secondresistor, an inductor, and means to connect said second resistor andsaid inductor in series between the cathode of said control tube and thecontrol grid of said oscilator tube to vary the impedance across thegrid and cathode of said oscillator tube in response to said variationsof said control voltage thereby to vary the frequency of said oscillatorabout said determined value.

3. A circuit arrangement for maintaining the frequency of an oscillatorconstant at a given value in response to a control voltage havingvariations'proportional to the frequency deviations of said oscillator,comprising an oscillator tube having an anode, a control grid and acathode, a resonant circuit coupled between the anode and cathode ofsaid oscillator tube to determine the frequency of said oscillator, acoil inductively coupled to said resonant circuit, a capacitor couplingsaid coil between the anode and cathode of said oscillator tube tocouple the grid in feedback relationship to the grid of said oscillatortube, a control tube having an anode, a grid and a cathode, the anode ofsaid control tube being coupled to the cathode of said oscillator tube,a first resistor, a second capacitor, means to connect said firstresistor and said second capacitor in series between the grid of saidcontrol tube and the cathode of said oscillator tube, means'to applysaid control voltage across said first resistor, a second resistor, aninductor, and means to connect said second resistor and said inductor inseries between the cathode of said control tube and the control grid ofsaid oscillator tube to vary the impedance across the grid and cathodeof said oscillator tube in response to said variations of said controlvoltage thereby to maintain the frequency of said oscillator constant atsaid given frequency value.

4. A circuit arrangement for maintaining the frequency of an oscil atorconstant at a given frequency value, comprising an oscillator tubehaving'an anode. a control grid and a cathode, a resonant circuitcoupled between the anode and cathode of said oscillator tube todetermine the frequency of said oscillator, a coil inductively coupledto said resonant circuit, a capacitor coupling said coil between thegrid and cathode of said oscillator tube to couple the grid in feedbackrelationship to the anode of said oscillatortube, a frequency responsivedetector coupled to said resonant circuit to derive a potentialproportional to the frequency deviation from said given frequency value,a control tube having an anode, a grid and a cathode, the anode of saidcontrol tube being coupled to the cathode of said oscillator tube, afirst resistor, a second capacitor, means to connect said first resistorand said second capacitor in series between the grid of said control 1tube and the cathode of said oscillator tube, means to couple saidfrequency responsive detector across said first resistor to apply saidpotential thereto, a second resistor, an inductor, and means to connectsaid second resistor and said inductor in series between the cathode ofsaid control tube and the control grid of said oscillator tube to varythe impedance across the grid and cathode of said oscillator tube inproportion to said potential thereby to maintain the frequency of saidoscillator at said given value.

5. A circuit arrangement for maintaining the frequency of an oscillatorconstant at a given frequency value, comprising an oscillator tubehaving an anode, a control grid and a cathode, a resonant circuitcoupled between the anode and cathode of said oscillator tube todetermine the frequency of said oscillator, a coil inductively coupledto said resonant circuit, a capacitor coupling said coil between thegrid and cathode of said oscillator tube, a frequency responsivedetector coupled to said resonant circuit, a control tube having ananode, a grid and a cathode, the anode of said control tube beingcoupled to the cathode of said oscillator tube, a first resistor, asecond capacitor, means to connect said first resistor and said secondcapacitor in series between the grid of said control tube and thecathode of said oscillator tube, means to couple said frequencyresponsive detector across said first resistor, a second resistor, aninductor, and means to connect said second resistor and said inductor inseries between the cathode of said control tube and the control grid ofsaid oscillator tube.

6. In an oscillator circuit arrangement in which the oscillator isadapted to be controlled by application of a control voltage, thecombination comprising an oscillator tube having an anode, a cathode andat least one control grid, a resonant circuit coupled between the anodeand cathode of said oscillator tube to determine the basic frequency ofthe oscillator, means coupling the anode in feedback relationship to thegrid of said oscillator tube, a reactance element interposed in thefeedback path between the anode and the grid of said tube and having agiven reactance value, an auxiliary grid-controlled discharge tube hav-7 ing a variable impedance of the same order of magnitude as aid givenreactance value coupled 7 between the cathode and grid of saidoscillator tube, and means to apply said control voltage to saidauxiliary grid-controlled tube whereby the frequency of said oscillatorvaries in response to said control voltage.

EGBERT SCHOLTEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,683,012 Appleby Sept. 4, 19281,997,084 Roosenstein Apr. 9, 1935 2,265,016 White Dec. 2, 19412,349,885 Roberts May 30, 1944 2,397,701 Smyth Apr. 2, 1946 FOREIGNPATENTS Number Country Date 166,594 Great Britain July 11, 1921Certificate of Correction Patent N 0. 2,531,301 November 21, 1950 EGBERTSCHOLTEN It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows: 7

Column 4, line 51 for anode read m'd; line 53, for rid read (mode a 9 gand that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOflice. Signed and sealed this 30th day of January, A. D. 1951.

THOMAS F. MURPHY,

Assistant Gammz'ssz'oner of Patents.

